Legumes () are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consumption, but also as livestock forage and silage, and as soil-enhancing green manure. Legumes produce a botanically unique type of fruit – a simple fruit Dry fruits that develops from a simple carpel and usually dehisces (opens along a seam) on two sides.
Most legumes have Symbiosis nitrogen-fixing bacteria, Rhizobia, in structures called . Some of the fixed nitrogen becomes available to later crops, so legumes play a key role in crop rotation.
Terminology
The term
pulse, as used by the United Nations' Food and Agriculture Organization (FAO), is reserved for legume crops harvested solely for the dry seed.
This excludes
and
Pea, which are considered
vegetable crops. Also excluded are seeds that are mainly grown for oil extraction (
like
and
),
and seeds which are used exclusively for sowing
forage (
,
alfalfa).
However, in common usage, these distinctions are not always clearly made, and many of the varieties used for dried pulses are also used for green vegetables, with their beans in pods while young.
Some Fabaceae, such as Scotch broom and other Genisteae, are leguminous but are usually not called legumes by farmers, who tend to restrict that term to food crops.
The FAO recognizes 11 primary pulses, excluding green vegetable legumes (e.g. green peas) and legumes used mainly for oil extraction (e.g., soybeans and groundnuts) or used only as seed (e.g., clover and alfalfa).
-
Dry beans (FAOSTAT code 0176, Phaseolus spp. including several species now in Vigna)
-
Dry Vicia faba (code 0181, Vicia faba)
-
Horse bean ( Vicia faba equina)
-
Broad bean ( Vicia faba)
-
Field bean ( Vicia faba)
-
Dry peas (code 0187, Pisum spp.)
-
Pea ( Pisum sativum var. sativum)
-
Protein pea ( Pisum sativum var. arvense)
-
Chickpea, garbanzo, Bengal gram (code 0191, Cicer arietinum)
-
Dry cowpea, black-eyed pea, blackeye bean (code 0195, Vigna unguiculata)
-
Pigeon pea, Arhar/Toor, cajan pea, Congo bean, gandules (code 0197, Cajanus cajan)
-
Lentil (code 0201, Lens culinaris)
-
Bambara groundnut, earth pea (code 0203, Vigna subterranea)
-
Vetch, common vetch (code 0205, Vicia sativa)
-
(code 0210, Lupinus spp.)
-
Pulses NES (code 0211), Minor pulses, including:
-
Lablab, hyacinth bean ( Lablab purpureus)
-
Jack bean ( Canavalia ensiformis), sword bean ( Canavalia gladiata)
-
Winged bean ( Psophocarpus tetragonolobus)
-
Velvet bean, cowitch ( Mucuna pruriens var. utilis)
-
Yam bean ( Pachyrhizus erosus)
Distribution
Legumes are widely distributed as the third-largest
land plant family in terms of number of species, behind only the
Orchidaceae and
Asteraceae, with about 751
genera and some 19,000 known species,
constituting about seven percent of flowering plant species.
Ecology
Nitrogen fixation
Many legumes contain
symbiosis bacteria called
Rhizobia within
of their
root (plants belonging to the genus
Styphnolobium are one exception to this rule). These bacteria have the special ability of fixing nitrogen from atmospheric, molecular nitrogen (N
2) into
ammonia (NH
3).
The chemical reaction is:
Ammonia is converted to another form, ammonium (), usable by (some) plants, by the following reaction:
This arrangement means that the root nodules are sources of nitrogen for legumes, making them relatively rich in nitrogenous and protein. Nitrogen is therefore a necessary ingredient in the production of proteins.
When a legume plant dies in the field, for example following the harvest, all of its remaining nitrogen, incorporated into inside the remaining plant parts, is released back into the soil. In the soil, the amino acids are converted to nitrate (), making the nitrogen available to other plants, thereby serving as fertilizer for future crops.
In many traditional and organic farming practices, crop rotation or polyculture involving legumes is common. By alternating between legumes and non-legumes, or by growing both together for part of the growing season, the field can receive a sufficient amount of nitrogenous compounds to produce a good result without adding nitrogenous fertilizer. Legumes are often used as green manure.
Sri Lanka developed the polyculture practice known as coconut-soybean intercropping. Grain legumes are grown in coconut ( Cocos nuficera) groves in two ways: intercropping or as a cash crop. These are grown mainly for their protein, vegetable oil and ability to uphold soil fertility.Shanmugasundaram (1991). 929058047X, Taipei : The Center. 929058047X
Pests and diseases
A common pest of grain legumes that is noticed in the tropical and subtropical Asia, Africa, Australia and Oceania are minuscule flies that belong to the family
Agromyzidae, dubbed "bean flies". They are considered to be the most destructive. The host range of these flies is very wide amongst cultivated legumes. Infestation of plants starts from germination through to harvest, and they can destroy an entire crop in early stage.
Black bean aphids are a serious pest to broad beans and other beans. Common hosts for this pest are fathen, thistle and dock.
Pea weevil and
bean weevil damage leaf margins leaving characteristics semi-circular notches.
are very widespread but will be found more frequently in areas where host plants are grown.
Common legume diseases include anthracnose, caused by Colletotrichum trifolii; common leaf spot caused by Pseudomonas syringae pv. syringae; crown wart caused by Physoderma alfalfae; downy mildew caused by Peronospora trifoliorum; root rot caused by Fusarium spp.; rust caused by Uromyces striatus; crown and stem rot caused by Sclerotinia trifoliorum; Southern blight caused by Sclerotium rolfsii; pythium (browning) root rot caused by Pythium spp.; fusarium wilt caused by Fusarium oxysporum; root knot caused by Meloidogyne hapla. These are all classified as biotic problems.
Abiotic problems include nutrient deficiencies, (nitrogen, phosphorus, potassium, copper, magnesium, manganese, boron, zinc), pollutants (air, water, soil, pesticide injury, fertilizer burn), toxic concentration of minerals, and unfavorable growth conditions.
Storage
Seed viability decreases with longer storage time. Studies of
vetch,
, and peas show that they last about 5 years in storage. Environmental factors that are important in influencing germination are relative humidity and temperature. Two rules apply to moisture content between 5 and 14 percent: the life of the seed will last longer if the storage temperature is reduced by 5 degree Celsius. Secondly, the storage moisture content will decrease if temperature is reduced by 1 degree Celsius.
Uses
Cultivated legumes encompass a diverse range of
Agriculture classifications, spanning
forage,
grain, flowering, pharmaceutical/industrial, fallow/green manure, and timber categories. A notable characteristic of many commercially cultivated legume species is their versatility, often assuming multiple roles concurrently. The extent of these roles is contingent upon the stage of maturity at which they are harvested.
Human consumption
Grain legumes are cultivated for their seeds,
for humans and animals to eat, or for oils for industrial uses. Grain legumes include
,
,
,
, and
.
Legumes are a key ingredient in vegan meat and dairy Meat analogue. They are growing in use as a plant-based protein source in the world marketplace.
There is a common misconception that adding salt before cooking prevents them from cooking through. Legumes may not soften because they are old, or because of hard water or ingredients in the pot; salting before cooking results in better seasoning.
Nutritional value
Legumes are a significant source of protein,
dietary fiber,
, and
dietary minerals; for example, a 100 gram serving of cooked
contains 18 percent of the
Daily Value (DV) for protein, 30 percent DV for dietary fiber, 43 percent DV for
folate and 52 percent DV for
manganese.
Legumes are an excellent source of resistant starch; this is broken down by gut flora in the large intestine to produce short-chain fatty acids (such as butyrate) used by intestinal cells for food energy.
Forage
Forage legumes are of two broad types. Some, like
alfalfa,
clover, vetch (
Vicia), stylo (
Stylosanthes), or
Arachis, are sown in
pasture and grazed by livestock. Others, such as
Leucaena or
Albizia, are woody shrubs or trees that are either broken down by livestock or regularly cut by humans to provide fodder. Legume-based feeds improve animal performance over a diet of perennial grasses. Factors include larger consumption, faster digestion, and higher feed conversion rate.
(1976). 089118046X, American Society of Agronomy. 089118046X
The type of crop grown for animal rearing depends on the farming system. In cattle rearing, legume trees such as Gliricidia sepium can be planted along edges of fields to provide shade for cattle, the leaves and bark are often eaten by cattle. Green manure can be grown between harvesting the main crop and the planting of the next crop.
Other uses
Legume species grown for their flowers include
, which are farmed commercially for their blooms as well as being popular in gardens worldwide. Industrially farmed legumes include
Indigofera and
Acacia species, which are cultivated for
dye and
natural gum production, respectively.
Fallow or
green manure legume species are cultivated to be tilled back into the soil in order to exploit the high levels of captured atmospheric nitrogen found in the roots of most legumes. Numerous legumes farmed for this purpose include
Leucaena,
Cyamopsis, and
Sesbania species. Various legume species are farmed for timber production worldwide, including numerous
Acacia species and
Castanospermum australe.
Some legume trees, like the honey locust ( Gleditsia) can be used in agroforestry.
History
and early modern humans used wild pulses when cooking meals 70,000 to 40,000 years ago.
Traces of pulse production have been found around the
Ravi River (Punjab), the seat of the Indus Valley civilisation, from 3300 BC. Meanwhile, evidence of lentil cultivation has also been found in Egyptian
Pyramid and
cuneiform .
Dry pea seeds have been discovered in a Swiss village that are believed to date back to the
Stone Age. Archaeological evidence suggests that these peas must have been grown in the eastern Mediterranean and
regions at least 5,000 years ago and in Britain as early as the 11th century.
The soybean was domesticated around 5,000 years ago in China from a descendant of the wild vine
Glycine soja.
The oldest-known domesticated beans in the Americas were found in Guitarrero Cave, an archaeological site in Peru, and dated to around the second millennium BCE.
International Year of Pulses
The International Year of Pulses 2016 was declared by the Sixty-eighth session of the United Nations General Assembly.
The Food and Agriculture Organization of the United Nations was nominated to facilitate the implementation of the year in collaboration with governments, relevant organizations, non-governmental organizations and other relevant stakeholders. Its aim was to heighten public awareness of the nutritional benefits of pulses as part of sustainable food production aimed towards
food security and
nutrition. The year created an opportunity to encourage connections throughout the food chain that would better use pulse-based proteins, further global production of pulses, better use
Crop rotation and address challenges in the global trade of pulses.
See also
Further reading
External links
